Gas-generating pyrotechnic composition consisting essentially of ammonium nitrate and aminotetrazole



United States Patent 3,348,985 GA-GENERATHNG PYRUTECHNIC COMPOSITION CONEBISTIING ESSENTIALLY 0F AMMONIUM NI- TRATE AND AMINUTETRAZGLE Hans Stadler and Kurt Ballreich, Nurnberg, and Heinz Gawlick, Forth, Germany, assignors to Dynamit Nobel Aktiengeseilschatt, Troisdorf, Germany No Drawing. Filed Aug. 4, 1966, Ser. No. 570,163 Claims priority, application Germany, Aug. 14, 1965, D 47,981 Claims. (Cl. 149-2) The present invention relates to improved pyrotechnic gas-generating compositions. More particularly, the present invention concerns inorganic nitrate gas-generating compositions which burn-off rich in gas, and are useful in pressure, gas-producing propellant charges, cartridges, missile propulsion, and other explosive applications.

Ammonium nitrate compositions which contain various additives which act as catalysts and/or control the reaction velocity are well known for use in ejecting fireextinguishing compositions from fire extinguishers. For such an application, cartridges are utilized containing a charge of an ammonium nitrate-containing mixture, which develops a substantial amount of gas when burning. The gas volume which is developed by such mixtures depends, to a large extent, upon the content of ammonium nitrate, which yields during the reaction predominantly gaseous nitrogen and water. Such a gas-producing composition may contain, for example, a high content of ammonium nitrate, i.e., about 78.5%, about 9% potassium nitrate, about 6.9% ammonium and about 5.6% potassium dichromate. This mixture is capable of yielding a gas volume of up to about 200 millimeters per gram of charge mixture. While this gas-producing mixture may find some application, for example, in fire extinguishers as discussed above, the yield of gas generated by this mixture and available for use is too low for many purposes and applications, such as a gas-producing propellant charge in cartridges, missile applications, etc., and thus its use is highly restricted.

In attempting to produce improved gas-generating compositions, various additives have been mixed with ammonium nitrate compositions. Not only have these additives failed to substantially improve the gas-generating capabilities of the ammonium nitrate composition, but undersirable side effects were also introduced. These side effects include, for example, materially increasing the reaction temperature and reaction velocity, impairing the ignitability of the mixture, adversely affecting the decomposition reaction of ammonium nitrate being catalyzed by ammonium dichromate,.and in some cases sensitizing the composition to the extent that it becomes an explosiondangerous substance. Furthermore, since for numerous applications the gases being produced should be substantially free from carbon monoxide, compounds having a high carbon content have not been considered in producing an improved gas-generating composition.

An object of the present invention is to provide an improved gas-generating composition which overcomes the disadvantages of the prior art.

Another object of the present invention is to provide an improved inorganic nitrate'containing, gas-generating composition capable of generating a substantial increase in gas yield.

A further object of the present invention is to produce an improved, gas-generating composition without materially increasing the reaction temperature, reducing the reaction velocity, and impairing the ignitability of the mixture.

A still further object of the present invention is to produce an improved, gas-generating composition which is Patented Oct. 24, 1967 ice not characterized as an explosion-dangerous substance, and wherein the catalyzing action of ammonium dichromate upon ammonium nitrate is not adversely affected.

Other objects and further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. It should be understood, however, that the detailed description and specific exam ples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.

Pursuant to the present invention, it "has been found that the above-mentioned disadvantages may be eliminated and a much improved gas-generating composition may be obtained by providing a gas-generating composition containing a mixture of ammonium nitrate and aminotetrazole. It has been found, for example, that an ammonium nitrate charge containing aminotetrazole increases the useable and effective gas volume by as much as about 100% and even higher. The ammonium nitrate present in the gas-generating composition of the present invention is present in a major amount of about 53 to 83% by weight, based on the weight of the total components of the composition, preferably about 60 to by weight. The aminotetrazole is present in a minor amount, i.e., about 2 to 25% by weight, advantageously about 5 to 15% by weight.

In a further embodiment of the present invention a part of the aminotetrazole present in the gas-generating composition of the present invention can be exchanged with other suitable nitrogen-containing compounds. Thus, for example, about 5 to 40% of the aminotetrazole can be substituted with a mixture of about 60 to 98% aminotetrazole and about 2 to 40% dicyandiamide. In addition to reducing the cost, the addition of this nitrogen-containing material improves the burning-off velocity and lighting power of the composition while not materially changing the volume of the gas being generated.

The ammonium nitrate used in the composition of the present invention may be of any type, for example, ordinary commercial ammonium nitrate, such as is used for fertilizers, or military grade ammonium nitrate. The commercial grade nitrate generally contains a small amount of impurities, and the particles of nitrate are usually coated with a moisture-resisting material, such as parafiin wax. Military grade ammonium nitrate which is almost chemi cally pure is particularly suitable for use in the composi tion of the present invention. The ammonium nitrate is preferably used in a finely divided particulate form, which may be obtained either by pulling or by grinding. The ammonium nitrate, gas-generating composition of the present invention frequently contains minor amounts of other inorganic nitrates, such as, for example, sodium nitrate or potassium nitrate. These inorganic nitrates can be present in an amount of about 6 to 9% by weight preferably about 6.5 to 8.5% by weight.

The present invention also contemplates the presence of a coolant, for example, ammonium oxalate, urea oxalate, ammonium nitrate, oxalic acid, oxamide, and the like, and an inorganic catalyst, for example, ammonium dichromate and the alkali and alkaline earth metal dichromates, e.g., sodium, potassium and magnesium dichromate. If the gas-generating composition contains coolants, they are present in an amount of about 5 to 7% by weight, preferably 5.5 to 6.5% by weight. When the dichromates are present, they are employed in an amount of about 4 to 6% by weight, preferably about 4.5 to 5.5% by weight.

The gas-generating composition of the present invention may optionally, and frequently, advantageously, contain other constituents. For example, ballistic modifiers can be used in the composition of the present invention to control the burning rate and to enhance the ignitability of the composition. Suitable ballistic modifiers include guanidine nitrate, nitroguanidine, cyclotrimethylenetrinitramine, 2,4-dinitrophenoxyethanol, and the like. Various burning rate promoters such as, for example, finely divided carbon, which are not catalysts per se may also be incorporated into the present composition. Oximes or asphalts may be used to improve low temperature ignitability. Aromatic amines are advantageously used as gas-evolution, stabilization additives. Examples of such aromatic amines are toluenediamine, diphenylarnine, naphthalenediamine, and toluenetriamine. In general, the aromatic hydrocarbon amines can be used in amounts of between about 0.5 and 5%. While these aromatic hydrocarbon amines are effective, they are frequently not sufficiently effective for severe duty when used alone. It has been found that superior stabilization is obtained when N-phenylmorpholine is used with an aromatic hydrocarbon amine. Because of the plasticizing effect of the N- phenylmorpholine, it is generally desirable to use the aromatic hydrocarbon amines as the primary stabilizing additive and the N-phenylmorpholine in an amount needed to obtain the specific stability. In general, when aromatic hydrocarbon amines are present, between about 0.1 and 1% of N-phenylmorpholine will be used.

Advantageously, all of the components of the gasgenerating composition of the present invention will have a grain size of less than 200 microns to faciliate intimate mixture or blending of the various components with each other and correspondingly achieve a homogeneous mixture, which assures uniform burning.

The ammonium nitrate compositions of the present invention are advantageously compressed into a compact form. The ingredients are intimately mixed and then consolidated under pressure by molding or extrusion at ambient or elevated temperatures. Depending upon the particular compositions and the desired density of the finished product, compression pressures of up to about 2,500 kg/cm. can be used to make the desired pellets. Producing compact pellets by this method produces a defined burning surface and achieves a desired burning velocity, and thus a uniform reaction mixture. Various types of conventional molding or extrusion apparatus are suitable for the purposes of the present invention. In some instances, it has been found desirable to add solvents to the gas-generating composition to facilitate the molding process. Solvents suitable for this purpose include hexane, heptane, cyclohexane, benzene, petroleum ether, and the like.

The pyrotechnic mixture of the present invention is useful as pressure, gas-producing, propellant charges in cartridges; as gas-generating compositions for use in jet propulsion, e.g., in the propulsion of rockets, ground-t0- ground missiles, ship-to-shore missiles, air-to-ground missiles; as a propulsion means in assist take-off of military and commercial aircraft, and many other uses.

The following examples more particularly define the present invention but are not to be considered as limiting.

Example 1 A pyrotechnic mixture is prepared by mixing 78.5% by weight of ammonium nitrate with 9% by weight potassium nitrate, 6.9% by weight ammonium oxalate, and 5.6% by weight of potassium dichromate. The components of the mixture, which have an average particle size of less than 200 microns, are thoroughly mixed to form a homogeneous mixture. The mixture is then formed into pellets using a conventional molding apparatus at a compression pressure of about 2,500 kg./cm. Upon burning, the composition yields a gas volume of approximately 200 cc. per gram of charge mixture.

Example 11 A pyrotechnic composition is prepared by mixing 66.7% by weight ammonium nitrate with 7.6% by weight potassium nitrate, 5.9% by weight ammonium oxalate, 4.8% by weight ammonium dichromate and 15.0% by weight of aminotetrazole. The mixture is pelleted in the same manner as in Example I. Upon burning, a gas volume of about 400 cc. is produced per gram of charged mixture.

Comparing Example I with Example II, it can be readily seen that the addition of aminotetrazole to the gas-producing mixture increases the available, useable gas volume by about The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention and all such modifications are intended to be included within the scope of the following claims.

We claim:

1. A pyrotechnic gas-generating composition comprising about 53 to 83% of ammonium nitrate and about 2 to 25% of aminotetrazole.

2. The composition of claim 1 wherein about 5 to 40% by weight of the aminotetrazole is replaced by a mixture of about 2 to 40% by weight dicyandiamide and 60 to 98% by weight of aminotetrazole.

3. The composition of claim 1 wherein all the components have a grain size of less than about 200 microns.

4. A pyrotechnic gas-generating composition comprising about 53 to 83% by weight of ammonium nitrate, about 6 to 9% by weight potassium nitrate, about 5 to 7% by weight ammonium oxalate, about 4 to 6% by weight ammonium dichrom-ate, and about 2 to 25% by weight of aminotetrazole.

5. The composition of claim 4 wherein about 5 to 40% by Weight of the aminotetrazole is replaced by a mixture of about 2 to 40% by weight dicyandiamide and 60 to 98% by weight of aminotetrazole.

6. The composition of claim 5 wherein all the components have a grain size of less than about 200 microns.

7. A process for producing a pyrotechnic mixture of improved gas-producing properties which comprises mixing together about 53 to 83% by weight ammonium nitrate, and about 2 to 25 by weight of aminotetrazole to form a homogeneous mixture, and forming said mixture into pellets by compressing them at a pressure of up to about 2,500 kg./cm.

8. The process of claim 7 wherein about 5 to 40% by weight of the aminotetrazole is replaced by a mixture of about 2 to 40% by weight dicyandiamide and 60 to 98% by weight aminotetrazole.

9. The process of claim 8, wherein about 6 to 9% by weight of potassium nitrate, about 5 to 7% by weight ammonium oxalate, and about 40 to 6% by weight ammonium dichromate are added to the reaction mixture.

10. The process of claim 9, wherein all the components have a grain size of less than 200 microns.

CARL D. QUARFORTH, Primary Examiner. S. J. LECI-IERT, JR., Assistant Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION atent No. 3,348,985 October 24, 1967 Hans Stadler et a1.

It is certified that error appears in the above identified patent and that said Letters Patent are hereby corrected as shown below:

line 59, "40 to 6%" should read 4 to 6% Column 4,

Signed and sealed this 8th day of September 1970.

(SEAL) Attest:

WILLIAM E. SCHUYLER, JR.

Commissioner of Patents Edward M. Fletcher, I r.

Attesting Officer 

1. A PYROTECHNIC GAS-GENERATING COMPOSTION COMPRISING ABOUT 53 TO 83% OF AMMONIUM NITRATE AND ABOUT 2 TO 25% OF AMINOTETRAZOLE. 